Interlayer interactions in M(OH)(2): A neutron diffraction study of Mg(OH)(2)

Magnesium hydroxide, Mg(OH)(2) M(r) = 58.3, trigonal, <P(3)over bar m1>, a = 3.148 (1), c = 4.779 (2) Angstrom, V = 41.015 Angstrom(3), D-x = 2.36 g cm(-3) at room temperature; a = 3.145 (1), c = 4.740 (2) Angstrom, V = 40.602 Angstrom(3), D-x = 2.39 g cm(-3) at 70 K; Z = 1, lambda = 0.8330 (5) Angstrom, mu = 1.78 cm(-1), F(000) = 9.503 fm; final R = 2.42, wR = 2.40, S = 3.22 for 82 unique reflections at room temperature; R = 1.84, wR = 1.82, S = 2.54 for 81 unique reflections at 70 K. Refinements have been carried out using anisotropic thermal coefficients for all atoms. To interpret the very large thermal motion of the H atom, subsequent refinements have been carried out with an anharmonic model and with a three-site split-atom model, and results are compared with those previously reported for Ca(OH)(2). By comparing the interatomic distances O ... O, H ... H and H ... O in the interlayer spacing of Mg(OH)(2) and Ca(OH)(2), as well as their temperature dependence, the nature and the strength of interlayer interactions in both compounds are discussed.